In the distant reaches of the Kuiper Belt, Pluto and its largest moon, Charon, boast strikingly diverse surfaces, yet their thermal and energetic mysteries remain unsolved. Scientists have struggled to accurately measure their temperatures because past observations blurred the two worlds together, making it hard to distinguish Pluto’s icy plains from Charon’s rugged terrain.
But the intrigue doesn’t stop there. Recent models suggest a hidden factor—Pluto’s atmospheric haze may be emitting light in the mid-infrared range, potentially skewing thermal readings even further.
NASA’s James Webb Space Telescope (JWST) has captured Pluto’s icy surface changes and an eerie phenomenon—material from Pluto’s atmosphere drifting onto Charon, its largest moon.
This bizarre interaction, unique to our solar system, was detailed in a series of new studies by an international research team.
Pluto ‘kissed’ its moon and captured it in orbit
After New Horizons’ Pluto flyby, UC Santa Cruz‘s Xi Zhang proposed in 2017 that Pluto’s atmosphere is dominated by haze particles, making it unlike any other in the solar system. He suggested that these particles heat up and cool down, controlling Pluto’s entire energy balance.
That crazy idea drew skepticism from fellow scientists. But the team made a bold prediction—if the haze cools Pluto, it should emit intense mid-infrared radiation, detectable once a powerful enough telescope becomes available.
Now, with JWST’s observations, that prediction may finally be put to the test. The 2017 hypothesis inspired the latest JWST study, and the results confirmed scientists’ predictions.
NASA’s New Horizons flyby in 2015 revealed Pluto as a world of rugged landscapes, nitrogen and methane glaciers, and a chemically rich atmosphere, similar to Saturn’s moon Titan, with haze formed by methane and nitrogen reactions.
Pluto’s atmosphere is slowly disappearing
Charon, in contrast, has no atmosphere and a surface dominated by water ice mixed with ammonia compounds. Its reddish poles likely result from methane escaping Pluto, which gets trapped and chemically altered on Charon.
Now, JWST’s powerful MIRI instrument has provided a fresh look at this distant system. For the first time, scientists have separately measured the mid-infrared thermal emissions of Pluto and Charon, capturing light curves at wavelengths of 18, 21, and 25 µm.
In May 2023, JWST recorded a high-quality mid-infrared spectrum (4.9–27 μm) of Pluto and its atmosphere, revealing unexpected chemical richness that deepens our understanding of Pluto’s atmospheric processes and icy origins.
New JWST observations have revealed how the surface temperatures of Pluto and Charon shift as they rotate, offering fresh insights into their thermal properties. By comparing these light curves with thermal models, scientists have identified key factors—such as thermal inertia, emissivity, and temperature variations—that shape Pluto’s ice distribution and drive atmospheric escape to Charon.
Icy dunes on Pluto reveal a diverse and dynamic dwarf planet
The data also confirmed a second prediction from Linfeng Wan, a former Ph.D. student of Zhang, showing that Charon’s rotational light-curve amplitude aligns with their 2023 study.
“Pluto sits in a unique spot in how planetary atmospheres behave,” Zhang explains. “This helps us understand haze in extreme environments—not just on Pluto, but also on Neptune’s moon Triton and Saturn’s moon Titan, which have similar nitrogen and hydrocarbon-rich atmospheres.”
But the implications go even deeper. Zhang points out that before oxygen built up on Earth 2.4 billion years ago, our planet’s atmosphere was mostly nitrogen and hydrocarbons, just like Pluto’s today.
Journal Reference:
- Bertrand, T., Lellouch, E., Holler, B., et al. Evidence of haze control of Pluto’s atmospheric heat balance from JWST/MIRI thermal light curves. Nat Astron (2025). DOI: 10.1038/s41550-025-02573-z
